docs: def is_installed(self, bug: Bug) -> bool:
          """
          Determines whether the Docker image for a given bug has been installed
          on the server.
          """
          r = self.__api.get('bugs/{}/installed'.format(bug.name))
  
          if r.status_code == 200:
              answer = r.json()
              assert isinstance(answer, bool)
              return answer
  
          # TODO bug not registered on server
          if r.status_code == 404:
              raise KeyError("no bug found with given name: {}".format(bug.name))
  
          self.__api.handle_erroneous_response(r)